Free Testosterone Calculator
Your total testosterone number is lying to you. Or at least, it’s only telling you part of the truth.
Most guys walk out of their annual physical with one number on a sheet of paper — total testosterone — and a doctor who either says “you’re fine” or “you’re low.” That number is the headline. It’s not the story.
The story is how much of your testosterone is actually doing anything. Most of it is bound up and unavailable to your body. A smaller fraction is free and working. Two men with identical total testosterone can feel completely different depending on how much of theirs is actually free.
That’s what this calculator shows you.
Calculate your free & bioavailable testosterone
Enter your total testosterone, SHBG, and albumin from a recent lab report. We’ll show you how much of your testosterone is actually free and bioavailable — and what that means.
Talk to a specialist about whether treatment is right for you.
For educational purposes only. These calculated values are reliable in most clinical situations but should not be used to make treatment decisions without a qualified clinician. The Vermeulen equation may be less accurate in cases of pregnancy, transdermal DHT use, oral testosterone, or other conditions affecting SHBG binding.
Why your total T number isn’t enough
Here’s what actually happens to testosterone in your bloodstream.
About 44–65% of it is locked up tight, bound to a protein called SHBG — sex hormone-binding globulin. SHBG grips testosterone like a vault. Once it’s bound, your body can’t use it. It’s just sitting there, padding your lab number.
Another 30–55% is loosely bound to albumin, a transport protein. This is the “weakly bound” fraction — your body can release it when needed and put it to work.
And only 2–3% is completely unbound. Floating free. Immediately usable. That’s your free testosterone, and it’s the most metabolically active form.
When you add free T to the albumin-bound fraction, you get bioavailable testosterone — everything your body can actually access.
Your lab report shows you total T, which is all three combined. It doesn’t tell you the split. And the split is what determines how you feel.
The high-SHBG trap
Here’s the case that catches everyone off guard.
A guy walks into a doctor’s office with classic low-T symptoms — tired, no drive, can’t recover from workouts, mood is in the dirt. His labs come back: total testosterone 720 ng/dL. The doctor says he’s fine. He’s not.
His SHBG is 80 nmol/L — well above the normal range. So most of his testosterone is locked up. His free T comes in at 8 ng/dL — below the typical adult male range. He has symptoms because his body can’t access most of what’s in his blood.
This is exactly the case the calculator is built to catch. The doctor who only checks total T misses it every time. And the patient walks away thinking he must be imagining things.
He’s not imagining things. The math just hadn’t been done.
What your numbers mean
Where you fall on total testosterone tells you something. Where you fall on free testosterone tells you more. Here’s how to read your results.
Total testosterone tiers
This is where traditional medical guidelines most consistently support TRT treatment. Men in this range frequently report fatigue, low libido, poor recovery, reduced strength, brain fog, depressed mood, and loss of motivation. If you’re here and have symptoms, you are very likely a TRT candidate.
A large percentage of symptomatic men seeking TRT fall here. Often associated with declining energy, reduced drive, inconsistent erections or libido, slower gym recovery, increased body fat, and feeling “off” despite technically being within lab range. Many modern TRT clinics consider this a reasonable treatment range when symptoms and supporting labs align.
You may not meet classic hypogonadism criteria, but men in this range can still experience reduced performance, slower recovery, lower resilience to stress, weaker training adaptation, and less mental sharpness compared to earlier years. This is where optimization-focused TRT conversations often begin — especially in men with low free testosterone or elevated SHBG.
If you have symptoms despite numbers in this range, the issue may be your free T. Check the calculator. If your free testosterone is below 9 ng/dL or your SHBG is above 45 nmol/L, your usable testosterone is lower than your total suggests.
Free testosterone reference range
Typical adult male range is roughly 5–21 ng/dL, with most healthy men sitting somewhere in the 9–18 ng/dL band.
Below 5 ng/dL is clearly low. Between 5 and 9 ng/dL is the gray zone where symptoms often appear. Above 21 ng/dL is uncommon outside of supplementation.
What is SHBG and why does it matter?
SHBG stands for sex hormone-binding globulin. It’s a protein made by your liver, and its job is to transport testosterone and estradiol through your bloodstream.
The problem is that SHBG doesn’t just transport testosterone. It grips it. Hard. Anything bound to SHBG is biologically inactive — your cells can’t use it.
So the higher your SHBG, the more of your testosterone is locked up and unavailable, even if your total T looks fine on paper.
What affects SHBG levels
A few things drive SHBG up:
- Age. SHBG creeps up over time. It’s one of the reasons free T declines faster than total T as men get older.
- Liver health. Your liver makes SHBG. Hepatic conditions tend to push it higher.
- Thyroid function. Hyperthyroidism elevates SHBG. Hypothyroidism lowers it.
- Insulin levels. Higher insulin tends to lower SHBG. Lean, insulin-sensitive men often have higher SHBG. Heavier, insulin-resistant men often have lower SHBG.
- Some medications. Certain anticonvulsants, oral estrogens, and other drugs can shift SHBG significantly.
The takeaway: SHBG isn’t a number you can will away with discipline. It’s largely metabolic and genetic. But knowing where yours sits is the difference between understanding your hormone picture and guessing at it.
Most primary care doctors don’t order SHBG. Most TRT clinics don’t either. That’s how guys with high-SHBG-driven low free T fall through the cracks for years.
How to get tested
Two paths, depending on where you’re starting from.
If you already have recent labs
Use the calculator above. You need three numbers from your lab report:
- Total testosterone (any of ng/dL, ng/mL, or nmol/L)
- SHBG (in nmol/L)
- Albumin (in g/dL or g/L — optional, the calculator uses the typical value of 4.3 g/dL if blank)
If your last lab panel didn’t include SHBG, that’s the most common gap. You can get just SHBG re-tested through us, or use one of our full panels below to get the complete picture.
If you don’t have labs yet
TRTPower offers three lab panels, designed for different starting points:
Total testosterone and a few essentials. Best for a first look at where you stand.
Note: Basic does not include SHBG, so you won’t be able to use the free testosterone calculator with this panel alone.
Total testosterone, SHBG, albumin, and a fuller hormone panel.
This is the minimum panel needed to use the free testosterone calculator. If you suspect a high-SHBG issue, start here.
Everything in Standard plus an expanded biomarker panel — thyroid, metabolic markers, full lipid breakdown, and more.
Best if you want the full picture in one shot.
Frequently asked questions
Can I have low free testosterone with normal total testosterone?
Yes — and it’s one of the most commonly missed scenarios in men’s health. If your SHBG is elevated, more of your total testosterone is bound up and unavailable. You can have a total T of 700 ng/dL and a free T below the reference range at the same time. Symptoms usually track the free T number more closely than the total. This is the exact case the calculator is built to catch.
What’s a healthy free testosterone level for a man?
Typical adult male reference range is roughly 5–21 ng/dL, with most healthy men in the 9–18 ng/dL range. Below 9 ng/dL is where symptoms tend to appear, even when total T looks fine. Below 5 ng/dL is clearly low. Like total testosterone, free T tends to decline with age — but the rate of decline varies significantly between men.
Why didn’t my doctor test SHBG?
Most primary care doctors don’t order SHBG routinely. It’s not part of a standard physical, and many haven’t been trained to think about testosterone in terms of the bound-versus-free split. The result is that men with high-SHBG-driven low free testosterone often spend years being told their labs look fine while their symptoms keep getting worse. If you have low-T symptoms and your doctor only ran total T, ask specifically for SHBG and albumin — or get them through us.
How accurate is this calculator?
The calculator uses the Vermeulen equation (1999), which is the most widely cited method for estimating free and bioavailable testosterone from total T, SHBG, and albumin. It’s used in major endocrinology research and clinical guidelines. Studies comparing Vermeulen-calculated free T against direct measurement by equilibrium dialysis — the gold standard — generally show strong agreement.
It’s less reliable in pregnancy, with transdermal DHT use, oral testosterone, or other conditions that significantly affect SHBG binding. For most adult men, it’s a reliable estimate.
Should I get on TRT if my free T is low but my total T is normal?
That’s a conversation to have with a specialist who looks at the full picture — symptoms, free T, SHBG, other hormones, and your goals. Some men in this situation benefit significantly from TRT. Others do better addressing the underlying drivers of high SHBG first. The honest answer is that it depends on you, and a quality consultation will give you a real recommendation rather than a one-size-fits-all answer.
Does the calculator work for women?
The reference ranges and tier interpretations on this page are calibrated for adult men. The Vermeulen equation itself works for any patient with valid total T, SHBG, and albumin values, but the “what your numbers mean” interpretation isn’t applicable to women, who have very different normal ranges.
What if my SHBG is low instead of high?
Low SHBG is less commonly discussed but worth knowing about. Men with low SHBG tend to have a higher percentage of their testosterone in the free fraction — which sounds good, but it often signals underlying issues like insulin resistance, obesity, fatty liver disease, or metabolic syndrome. If your SHBG is below 15 nmol/L, that’s worth investigating with a doctor regardless of your testosterone numbers.
Stop guessing at your hormones.
If you’ve gotten this far, you already suspect something’s off. The hardest part isn’t deciding whether to do something about it — it’s finding a clinic that looks at the whole picture instead of glancing at one number and sending you home.
TRTPower checks total testosterone, free testosterone, SHBG, and the full hormone panel that actually tells you what’s going on. We monitor you on an ongoing basis, not just at your initial consult. And we work with specialists who treat testosterone optimization as their primary focus, not a side concern.
Talk to a TRT specialist →This calculator and the information on this page are for educational purposes only. The Vermeulen equation produces reliable estimates in most clinical situations but should not be used to make treatment decisions without a qualified clinician. Reference ranges cited are typical adult male ranges and may vary by laboratory.